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Monday, August 31, 2009

Jason Perry has a nice summary of the Io white papers at his website: Io Decadal Survey White Paper. There are actually two white papers, one which discusses science goals and one which discusses possible missions. Neither had anything particularly new, and Jason does a good job of summarizing them. The most interesting part of the discussion was the endorsement of the Io Volcano Observer Discovery proposal (~$450) and in the next breadth discussing New Frontiers (~$650M)missions to conduct essentially the same goals. My guess -- no knowledge -- is that the community is nervous about the mission fitting within the Discovery budget. The last budget estimate I saw for the Io Volcano Observer put it slightly over the Discovery budget limit. The key issue, I would guess, is likely the technological risks of the radiation hardening fitting in the budget with acceptable margins.

An Io observer mission requires a plutonium power supply. The next Discovery mission can include such a plutonium power supply (to test the ASRG supply) while the next New Frontiers mission will not (to husband dwindling plutonium supplies). If an Io observer cannot fit into a Discovery budget (or can, but isn't selected), then the next opportunity is the late 20 teens New Frontiers opportunity. That would put Io in competition with the proposed Argo mission to Jupiter, Saturn, Neptune, Triton, and one or more Kuiper Belt objects (as well as other good missions to non-outer planet destinations.)

The key issue for any dedicated Io mission, however, is the planned flybys of Io by the Jupiter Europa Orbiter (JEO). A dedicated mission would provide much better Io science through optimized instruments and many more flybys, but will the community accept a flagship mission to Jupiter and another Jovian dedicated mission (given the Juno Jupiter polar orbiter and JEO)? My guess is not. If JEO proves too expensive to fly, then I think that a dedicated Io mission has a good shot.

Sunday, August 30, 2009

For some months now, a group of planetary scientists have been promoting a mission called Argo that would launch a flyby spacecraft (think of Voyager with 2010s instrumentation or New Horizons with a different set of targets and an expanded instrument suite). The mission would take advantage of an alignment of the outer planets that would allow launch of a craft in 2015 through 2020 that would use gravity assists from Jupiter and Saturn to enable a fly through of the Neptune system in the late 2020s followed by one or more Kuiper Belt Object (KBO) flybys. (The three papers show different mission options with different times

Three white papers have been posted detailing the science that might be done at Neptune, Triton, and the KBO(s). Details on the spacecraft and mission flight opportunities are minimal. The goal of the white papers is to have this mission prioritized high enough to get on the short list of allowed targets for New Frontiers (~$650M) missions, which are expected to be selected twice each decade. Currently, NASA expects to select a New Frontiers mission in the mid to late 2010s that might allow Argo to take advantage of this planetary line up. Unlike New Horizon which will have a limited selection of KBO's to visit following its Pluto flyby, Argo can use Neptune's gravity field to deflect the craft to a large space to enable selection of a potentially large set of KBOs. (Mentioned in passing, however, is the limitation that enabling a close flyby of Triton would limit the potential retargetting opportunities for KBOs. Mission designers would have some flexibility -- Triton can be encountered in different locations in its orbit -- but ultimately there is likely to be a trade off.)

An aggressive instrument list is published in the three white papers. The instruments cover the capabilities of the New Horizon's Pluto spacecraft and add color imaging for the high resolution instrument, a thermal imager, and a magnetometer.

No science goals are listed for the Jupiter and Saturn flybys, although one could expect similar science to what was performed by New Horizon at Jupiter. Ideally, the craft could determine whether or not the Enceladus plumes are still active several years after Cassini's demise.

The following charts are reproduced from the white papers. Each science goal is discussed in more detail in the papers, and I urge you to check them for more information

Thursday, August 27, 2009

Many of the Decadal Survey White Papers focus on specific missions or area of scientific investigation. However, missions can fly and conduct science only if the technologies required are available. One paper, "Technologies for Outer Planet Missions" lists a the technology investments needed to enable the post Jupiter Europa Exploration of the outer planets. It covers everything from aerocapture (to enable a Neptune mission), to advanced batteries, and in situ instruments. This is the absolutely necessary yeoman work necessary to enable planetary exploration.

Two sections of the white paper focuses on technology development necessary for future in situ Titan exploration. Reading these sections suggests that these concepts need technological maturation before they will be ready to fly. However, these paragraphs also give an idea of the types of missions that might be flown once the technology is ready (budgets permitting).

MobilityPrevious studies have identified the montgolfière balloon as a key element in a comprehensive Titan exploration strategy with very high science value. The most recent 2008 joint NASA/ESA Titan Saturn System Mission (TSSM) study provided a compelling concept for implementation of a montgolfière at Titan. While orbiter and lander elements appear to have significant flight heritage, a balloon has not been flown on Titan and will require focused study and risk reduction efforts. Based upon the high priority of Titan science, results from many years of mission studies, and current state of technology readiness, NASA and ESA review boards have recommended the following be pursued to enable a balloon mission at Titan within foreseeable budgets and at acceptable risk: 1) conduct focused studies of Titan balloon mission options, leveraging from previous work, to focus on selection of architecture(s) that best achieve highest priority science and 2) initiate substantial sustained investment in risk reduction efforts needed to mature the Titan balloon concept for flight readiness. Risk reduction efforts include the following: balloon deployment and inflation, thermal performance margins, packaging and thermal management inside the aeroshell, interface complexity between balloon, RPS and aeroshell and integration of the RPS into the balloon.Additionally, long-term operation of mobile platforms would be faced with challenges because of the long latency in communications, communications blackouts due to Titan rotation and occlusion by Saturn, the absence of a magnetic field, low surface illumination conditions, and the lack of high-resolution orbital maps. Consequently, autonomous navigation and control and autonomous onboard science capabilities for data prioritization and opportunistic observations will be critical. Linking scientific observations to their coordinates on Titan would significantly enhance the science value of an in situ mission. OPAG recommends a sustained investment in this decade that would result in the demonstration of technical readiness for launch of a Titan balloon mission. Further OPAG recommends that NASA fund the development of key autonomy capabilities required for a Titan balloon.

LandersThe geological, geophysical and presumed geochemical diversity of Titan’s surface suggest at least three surface types that should be sampled by a future mission to Titan: 1) a Titan lake lander/submersible that would land on a Titan sea e.g. Kraken Mare to measure the soluble hydrocarbon, nitrile, and noble gas content, isotopic composition and determine the lake level 2) a dune lander that could determine the interior structure, subsurface characteristics and tidal deformation as well as the composition of the dunes in hopes of understanding the fate of Titan’s organic aerosols that constantly rain down on the surface, and 3) a lander positioned near suspected cryo-volcanic structures to make seismic measurements and to follow the evolution of organic chemistry anticipated when Titan organic aerosols are exposed to liquid water. In all cases, the objectives involve geophysical measurements as well as sampling and analytical chemistry in a cryo-environment. Furthermore, the lake lander/submersible and the cryo-volcanic lander would require unique designs for such planetary environments. OPAG recommends that NASA invest in focused studies of these lander concepts and mature the technologies required to fulfill the science requirements.

Tuesday, August 25, 2009

Given the tight budgets for planetary exploration, I worry that large flagship missions to the outer planets may never fly. The current strategy is to fly ~$3B flagship missions once a decade: first the Jupiter Europa orbiter (JEO), then a Titan Saturn orbiter, and then possibly at Europa lander (if JEO finds a location with interior materials at or near the surface that is safe to land at). At the moment, NASA's planetary program would have to forgo either the Mars program or the Discovery/New Frontiers programs to pay for a $3B flagship mission. (Alternately, NASA could give up portions of both programs, but the point is that $3B missions can't be afforded without giving up something else.) (This is a topic I've addressed before in this blog entry: http://futureplanets.blogspot.com/2009/05/what-next-for-titan.html.)

I'd propose an on-going program of modest Titan missions carried out by multiple space agencies. A Titan lake lander could be a stand alone mission to provide compositional information. However, most other missions would require a data relay from an orbiter. NASA has made communications relay at Mars a priority (albeit also including scientific instruments on the orbiters) to enable high bandwidth communications with rovers. As a thought experiment, I would propose a similar strategy for Titan with each specific mission constrained to $650M to $1B. The key and first element would be a Saturn orbiter to provide communications relay and whatever scientific measurements would fit within the mission budget. (If affordable, my favorite would be a camera optimized to take advantage of the spectral windows in Titan's atmosphere for surface mapping.) The orbit initially might be chosen to optimize Titan flyby science and then later communications from Titan landers and balloons (although the same orbit might accomplish both). The orbiter might be a near twin of a Galilean icy moon observer to save costs. Given Cassini's long life, it would be reasonable to plan for a lifetime of a decade in orbit at Saturn. See this blog entry for examples of the science that a multi-flyby orbiter might be able to carry out.

After the relay is in place, several in situ missions could be flown:

A Titan lake lander for chemical measurements of the lake and atmosphere. While the main experiments might be battery powered and therefore short lived, a small plutonium power source would enable long-lived geophysical and meteorological measurements.
A geophysical network of landers for solid surface measurements powered by plutonium power sources to enable a lifetime of months to years.
One or more balloons to explore the atmosphere and make remote studies of the surface
Highly capable landers to carry out surface composition studies, possibly even with modest (to keep costs within reason; perhaps a couple of hundred meters) roving capabilities.

The Saturn orbiter would have to launch and arrive first. The order and timing of the subsequent missions could be dictated by launch opportunities and budgets. Breaking the missions up would allow multiple space agencies to contribute specific missions, spreading total costs among multiple nations.

A key difference between exploring Titan in small missions and doing the same at Mars is the flight times. Whereas Mars is months away, Titan is years. That alone would make each element more expensive. Data rates from the relay craft would be much lower than from Mars given the distance. This is one reason that the Saturn Titan orbiter is so expensive compared to Mars orbiters -- it needs lots of power to return high resolution mapping data. The modest Saturn orbiter in this thought experiment would have lower data rates than a flagship mission.

Closing Notes: Many really smart people have and will look at Titan exploration options. I'm under no illusion that I have ideas that are novel or that the ideas presented here are the best way to take advantage of limited budgets. I present them in the spirit of showing possibilities so that you can reach your own conclusions. As I did with the proposal for a Galilean Satellite observer mission, I'll publish thoughtful critiques of these ideas that are e-mailed to me at vkane56[at]hotmail.com.

Titan is the best atmosphere in the solar system for ballooning. The atmosphere is cold and dense, making a hot air montgolfiere balloon simple and providing a long descent time to inflate the balloon. The sun is far away, meaning that little solar heat arrives at Titan, reducing the diurnal heating of the balloon and the subsequent stress on the balloon material. However, a number of technical issues have been identified that require further work before a mission could be flown. These include balloon deployment and inflation and packaging of the balloon and it radioactive power source. These issues are being worked with a goal to achieve flight readiness by 2015. The goal is a system that can circumnavigate Titan at least once (3 to 6 months) but that might have a lifetime of years.

The white paper lists a number of investigation firsts that would be enabled by a balloon carrying a sophisticated (i.e., large) payload:

"1. First analysis of the detailed sedimentary record of organic deposits and crustal ice geology on Titan, including the search for porous environments (“caverns measureless to man”) hinted at by Cassini on Xanadu.
2. Direct test through in situ meteorological measurements of whether the large lakes and seas control the global methane humidity, which is key to the methane cycle.
3. First in situ sampling of the winter polar environment on Titan, a region expected to be vastly different from the equatorial atmosphere explored by Huygens.
4. Compositional mapping of the surface at scales sufficient to identify materials deposited by fluvial, aeolian, tectonic, impact, and/or cryovolcanic processes.
5. First search for a permanent magnetic field unimpeded by Titan's ionosphere.
6. First direct search for the subsurface water ocean suggested by Cassini.
7. First direct, prolonged exploration of Titan’s complex lower-atmosphere winds.
8. Exploration of the complex organic chemistry in the lower atmosphere and surface liquid reservoirs discovered at high latitudes by Cassini."

The paper lists the one major problem with a Titan balloon mission. Imaging of the surface with cameras and spectrometers would require a relay craft in orbit around Saturn or Titan. (Chemical analyses of the atmosphere, atmospheric structure (e.g., pressure) measurements could probably be acheived with direct to Earth communications. Perhaps even ice penetrating radar measurements could be taken without a relay orbiter; I'm not sure how much data this instrument would generate.) The white paper assumes a highly capable orbiter similar to the Titan Saturn orbiter that would cost approximately $3B. As long as a balloon mission is tied to an expensive flagship mission, I don't believe this mission will arrive at Titan until the 2030s. In the next blog entry, I'll do a thought experiment about an alternative approach.

Friday, August 21, 2009

This blog entry will begin a series of summaries of Decadal Survey White Papers. These position papers are submitted by members of the planetary research community to make the case to prioritize specific lines of inquiry, measurements, and missions. Because the papers are meant to be read by a wide audience, they generally are not too technical on either the science or engineering sides. This makes them readable by interested members of the general public such as myself and probably most of the readers of this blog. The papers are also short. The papers are limited to seven pages and 12 point font. All papers are due by September 15, meaning that there will soon be a flood of publication to the White Paper website. Drafts of a number of papers have been posted, and I'll begin summarizing these.

A couple of notes, though. I cannot publish summaries in anything approaching real time (the penalties of a family and career). You can probably expect that I will still be writing summaries for the next several months. Nor am I likely to read and summarize all the papers -- there is likely to simply be too many. However, all the White Papers are available at this website, so you can read the ones of greatest interest to you.

I'll start this series with a White Paper written by Ralph Lorenz (with a number of co-authors). Lorenz is a much published scientist who focuses on Titan and also has led or participated in a number of task forces exploring mission options for future Titan exploration. He has published a couple of books on Titan for the general public. Ralph is also a good guy to share a beer with at a scientific conference.

Lorenz's paper is, "The Case for a Titan Geophysical Network Mission." The goal of the paper is to have the Decadal Survey prioritize this mission high enough that it would make the list of potential missions for a future New Frontiers ($650M) class mission. A second goal is to make the development of small plutonium powered energy sources a priority. (NASA is considering developing such a power source to enable small probes to a number of solar system targets.)

This proposal is one of a number of proposals to establish long-lived (at least months, preferably years) networks of fairly small landers on a moon or planet. A number of fields of study such as meteorology, seismology, and rotational state require measurements from multiple locations on a surface. This paper lists several areas of study that could be advanced with simple Titan landers:

Measure near-surface meteorology for both short-term changes, medium-term changes from the atmospheric gravitational tide as Titan orbits Saturn, and potentially long-term changes with the passing of the seasons

Variations in Saturn's magnetic field on the surface of Titan to explore the properties of the water-ammonia ocean beneath Titan's crust

Track changes in Titan's rotation and tilt to explore the interior structure

Possibly make seismic measurements (which would require a relay orbiter)

The paper points out that the basic measurements could be made with sensors common in many high end watches: "a pressure sensor, a magnetometer, a light sensor, and a thermometer." If budgets allow, the landers could also carry a tiltmeter to study tidal deformation of the crust, a wind instrument, a seismometer, a communications system that allows precise doppler tracking, and a wind measurement instrument. A descent camera could take images of the landing site.

The paper is short on specifics, leaving the detailed definition to the proposers of an actual New Frontiers mission. Instrument mass could be as low 1.5 kg to 20 kg. The mission would fly four probes to Saturn on a carrier craft that drop the probes off without entering Saturn or Titan orbit. Communications would be direct to Earth, which would limit the bandwith to as little as 1 bit per second.

The delay of the Mars Science Laboratory Curiosity allows for additional landing sites to be considered. A call for proposals has been posted at http://marsoweb.nas.nasa.gov/landingsites/index.html. To save you the trouble of downloading the Word document, I've reproduced the letter below:

Dear Colleague:We invite you to take advantage of an opportunity to propose new candidate landing sites for the 2011 Mars Science Laboratory (MSL) mission. Addition of any new site to the list of four currently under consideration (Eberswalde crater, Gale crater, Holden crater, and Mawrth Vallis) will require both mineralogic and morphologic evidence demonstrating a compelling argument that it is at least as promising as the sites currently being evaluated. Moreover, the engineering or safety aspects of any candidate site must eventually be shown (by the MSL Project) to equal or exceed those of the four sites under consideration. Interpretations of the science potential of new candidate sites must be mature and would ideally be peer-reviewed and published prior to formal addition as a new candidate site.Consideration of new candidate sites requires preparation of an abstract that includes detailed information on the location and nature of the site. Specific requirements for proposing a new site and associated science and engineering criteria that must be included/discussed can be found in the abstract template posted at: http://marsoweb.nas.nasa.gov/landingsites/ and http://webgis.wr.usgs.gov/msl. Abstracts describing new sites should be submitted via e-mail to John Grant (grantj@si.edu) and Matt Golombek (matthew.p.golombek@jpl.nasa.gov). New candidate sites must be proposed by October 31, 2009 to be considered.We anticipate that an initial review for compliance to site requirements will be completed in early fall and that targets for initial imaging by MRO (or additional imaging if some MRO data already exists) will be submitted soon thereafter. These MRO data (HiIRSE, CRISM, and CTX) will be made available to persons proposing candidate sites to permit more comprehensive evaluation of their merit over the winter of 2009/2010. A review of remaining candidate sites in May of 2110 is anticipated and will likely involve presentations to the Landing Site Steering Committee and the MSL Project Science Group. This schedule is driven by Project requirements for initial assessment of any new candidate sites and the desire to obtain additional MRO data of any site added to the list under consideration in time for broader community discussion during the 4rd Workshop in September, 2010.We look forward to the continuing participation of the science community in MSL landing site activities and hope that you will consider and propose any new candidate sites which might help to maximize the science done by MSL.

I think GSO would be an excellent idea if JEO is to costly. Galileo, while it made fascinating discoveries, was horribly crippled by its antenna troubles. Not only is the data coverage thin, but because the data returned was so selectively targeted, the chances at serendipitous discovery were greatly reduced. Having followed the Cassini orbital tour, it is now even more painfully obvious what we missed. In addition to much more complete multispectral mapping of the four Galileans and Io monitoring (and searching for plumes on Europa, this spacecraft would be well equip to send back the atmospheric movies of Jupiter that Galileo could not. Plus, it could do the initial sounding of Europa to determine the thickness of the ice.

Granted, JEO has its Galileo-like tour, but the mission has a very finite end - it can't last too long in Europa orbit. GSO may well last as long as or longer than Galileo. Yes, there will be major sacrifice at Europa, but while I find Europa interesting, I fail to see why it it is so much more interesting than Io and even Ganymede. The four Galileans compose a system, and I don't think we have reached a point where we should focus so heavily on just one member.

I will admit that there is another thing infecting my thoughts. I would really like to see some more extensive studies of Io, and GSO might well return as Galileo did late in its mission for some more in-depth studies. There is no expanding JEO's tour. If a Discovery (with the Stirling RTG) proposal like the Io Volcanic Observer is chosen, my views on GSO would change considerably.

John R., who always seems to have thoughtful responses, sent the following response to my proposal, which I publish with his permission:

The perfect is the enemy of the good... and vice versa. The question is which to root for.

In this case, I'd hold out for perfect. An orbiter that has half the cost has to have more than half the scientific value, and this wouldn't cut it.

In my opinion, any jovian mission that doesn't orbit Europa has to play some very distinct role for relatively cheap (eg, Juno, much cheaper than JEO), or I'd recommend tabling the jovian system indefinitely. Aside from Juno, the only cheap alternative I could see would be something that stays totally out of the radiation belts for most of its main mission and observes Io over long periods of time with incidental observations of Callisto and Ganymede up-close. Maybe finish the mission with some deep-dives that reveal Io closely with passes by Europa along the way. But only if this is as cheap as Juno.

The way I see it, we're engaged in expensive games of Twenty Questions with Venus, Mars, Europa, Titan, Enceladus, Neptune/Triton, and other targets, with varying levels of priority and difficulty. We're necessarily going to be ignoring some of these targets. I'd have no sacred cows about which avoid being ignored and emphasize that every question *counts* -- maximally. Any place where the funding climate (or other factors) preclude us from asking a question that is worth the expense, we should sadly put on the Ignore list and let something else percolate up. Venus has taken the interminable delays for quite a while now. Mars even experienced that. It's going to happen to all of them.

Europa is actually the one place on the list where it might be most certain what the next mission should be. (Mars is a bit clouded by the variety of options; Neptune also seems to have some clarity about it, but loses out in terms of priority/difficulty.) Europa would be the one place where I'd most hate to have us satisfice.

Venus and Mars lend themselves most easily to satisficing; we can isolate individual scientific questions for a fixed price without making a massive commitment. My sense of the big picture would be to say that JEO, a modest mission to Venus (atmospheric probe that definitively nails down the isotopic abundances and does spot observations of the surface), and whatever comes next at Mars (a big issue in itself) are the *only* options I'd put on the table for major missions, and I'd drum my fingers on the table and take longer development periods towards fewer launches until those move through the queue.

The beauty of the Twenty Questions approach is that it can lend clarity to what comes next. It could tell us that Europa might merit hogging the pipeline for a while, or that it should be bumped far down the list. If we only observe 15% of Europa's surface closely, we might remain as uncertain as we are now.

Any Galilean [observer] mission might delay an eventual JEO. I don't find any intrinsic value in science at Target X over Target Y such that we need to visit Target X on a timely fashion to keep the pipeline going. If a mission has half the cost of JEO and less than half the science value, then I would NEVER fly it, ever, unless the rest of the solar system utterly lacked for alternatives (which isn't apt to be anyone's conclusion). I would fly fifty consecutive missions to Mars, if that's what it came to, rather than one to the Galileans that doesn't set up the next Galilean mission. Since JEO planning is mature, I would never fly any mission that is preparatory to JEO unless it had a clear cost/benefit advantage. Eg, if it returns 25% the science value, then it has to be under 25% the cost. Which seems likely to be impossible. So I'd never fly Galileo II.

Thursday, August 13, 2009

This message board is about future planetary exploration and the political factors that enable it or prevent it. From what I can tell of the budgeting process for NASA, the White House and Congress decide on a top level figure for NASA and divide that amount of money among competing programs such as the manned spaceflight program and the planetary program. (There's some give and take -- NASA appears to develop bottoms up budgets to take to the negotiations with the White House about the top line budget.)

An article at Spaceflight Now nicely summarizes the impossible situation the manned spaceflight program is in. The White House and Congress may decide to provide more money to NASA to help resolve these problems. Even if they do, the pressure to move money from the science side of NASA -- which includes the planetary program -- is likely to be intense. My prediction is that the planetary program will gradually shrink over the next decade. I hope that the Decadal Survey includes that possibility in their prioritization of planetary missions.

You are, of course, correct in pointing out that beggars can't be choosers, and the NASA planetary program looks more beggarly every day. It's entirely possible that we may end up having to settle for "Galileo 2.0", including just a handful of Europa flybys. If we do, however, among the most likely targets would be not just areas of particular interest to the ice-penetrating radar, but regions that may already be regarded as among the more promising locations for a lander and need to be characterized in more detail -- by high-res imaging (to sample fine-scale surface roughness and thus try to put lower-res images in context) and by VNIR spectrometry (to try to identify non-ice materials). Note that the VNIR spectrometer is one of only two instruments on EJSM to have an ability to slew its viewfield from side to side and thus widen its area coverage.

One of the main organizers of the Europa Focus Group meeting asked the sum total of assembled scientists in the room (and there were a lot) whether anyone thought this kind of intensive study of Europa would be justified if the place didn't have biological significance. Dead silence followed. Europa Orbiter is intended strictly as necessary advance preparation for the next mission, the big Europa Astrobiology Lander that would touch down and analyze the upper layers of the ice (perhaps down as deep as 100 meters or so, if it does its sampling with a short-range cryobot) for evidence of life.

Now, EO officially has two main purposes. One is to nail down once and for all absolute proof that Europa DOES have an ocean. A Jupiter orbiter cannot use a laser altimeter to make adequately sensitive measurements of the degree of tidal flexing of Europa's crust to answer that question -- but the induced magnetic field measurements of Galileo have almost totally nailed it down already. In fact, William McKinnon reported that the latest analyses of Galileo's data have flatly ruled out the slightest possibility that the field it detected was produced by any conductive material that wasn't in a layer very close to the surface. Indeed, the thickness of the layer indicated by the latest analysis of it is so thin -- maybe only 20 km thick -- that even seawater isn't conductive enough to generate the field unless a large amount of sulfates are dissolved in the water (which, of course, is precisely what the near-IR spectra of Europa's ice also indicate). A flyby craft with a magnetometer, making far more flybys of Europa targeted for this purpose than Galileo did, would surely get enough more induced-field measurements to nail this down even more solidly. We'd need repeated simultaneous data from two magnetometers in different places to be able to use it to gauge the thicknesses of the ice layer and the ocean itself, but that data is not in itself necessary to plan the Astrobiology Lander (which I will hereafter call EAL).

The other main purpose of EO is to find good landing sites for EAL. It would obviously be of huge assistance in that -- but if we're really strapped for money, we need to ask whether EO is absolutely necessary to pick out a good first landing site for EAL. Torrance Johnson, at the last astrobiology conference at Ames Research Center, said flatly that he thinks we can pick out a satisfactory first one just from the limited data we've already gotten from Galileo. That seems highly doubtful to me -- but a follow-up Jupiter orbiter with a properly working high-speed data link could do a lot of additional reconnaissance for such sites during its flybys of Europa, quite possibly enough for us to find a pretty satisfactory place even without full-scale coverage of Europa from an EO. It would unquestionably carry a high-resolution camera, a thermal mapper to look for any recent sites of vented water, and a near-IR spectrometer to map the makeup and concentration of materials that had oozed up to the upper ice from the ocean underneath -- and the likely spot for EAL will be one where that concentration is high, and where the lack of surface cratering and regolith suggests that the surface material has been exposed to Jupiter's radiation for only a relatively short time. It could map a lot of Europa just with those instruments.

There seems to be serious question as to whether or not such a flyby craft could get meaningful data from ice-penetrating radar -- even for just a few short strips of Europa's surface. But, again, while IPR is obviously extremely important for general studies of Europa, we have to ask whether it is absolutely necessary to pick out the best landing site for EAL, given the data we'll get from those other instruments. The main relevance of IPR for that particular purpose would be to try to locate pockets or fissures of liquid water very close to the surface -- within just 100 or 200 meters. But it might be possible to at least detect -- and map the horizontal extent of -- pockets of liquid water that close to the surface in a lot of places with a relatively insensitive, shallow ice-penetrating radar of the sort that a flyby craft MIGHT be able to use, even if it didn't measure the actual depth below the surface of such pockets beyond telling us that they were near-surface. And such a less ambitious and sensitive radar instrument used from a flyby craft might also be able to measure both fine-scale surface roughness -- very important data in picking out the EAL landing site -- and also the content of other material (rock dust and salts) in the ice, which could be very important in designing any sampling cryobot carried on EAL.

So, if we're as seriously strapped for cash as we now seem to be, it might -- repeat, might -- be feasible to replace EO with such a cheaper and simpler "Galileo 2" Jupiter orbiter that could survey not only Europa but also Ganymede, Callisto and maybe Io, as all the advance preparation we'd need to then jump straight to the Astrobiology Lander as the next Europa mission.

Tuesday, August 11, 2009

My thoughts on a Galilean Satellite Observer have prompted two thoughtful responses from readers that I'll post over the next couple of days. Before doing so, I wanted to share my intellectual basis for a Jovian icy moon observer. The National Academy of Sciences reviewed possible missions for the New Frontiers program and prioritized a Ganymede Observer as a candidate mission. (An Io observer was also prioritized, but it would ideally have instruments suited to a silicate world rather than an icy moon. So this post will concentrate on an icy moon observer.) The text below is copied from the working group's 2008 report, Opening New Frontiers in Space: Choices for the Next New Frontiers Announcement of Opportunity.

My thinking is that if a Ganymede multiple flyby mission is a priority, then a simple extension of that mission to flyby multiple Jovian moons would be even more valuable (assuming that the Jupiter Europa Orbiter doesn't fly, which I hope it does but budget realities my decide otherwise). As you'll see, these two readers either only partially agree or completely disagree. I'll present all sides of the argument so you can form your own opinion.

From the report:

Ganymede ObserverLarge icy satellites may hold the key to answering many fundamental questions about the solar system, and Jupiter’s largest moon, Ganymede, is of particular interest because of its unique internal magnetic field and its interaction with Jupiter. Ganymede is the only icy body in the solar system known to generate its own magnetic field, thus providing a unique window into its interior and, moreover, shedding light on how internal magnetic fields are generated elsewherein the solar system. Ganymede also provides a laboratory for the study of plasma effects on satellite surfaces: the decadal survey notes that “Ganymede’s magnetic field is strong enough that it creates a mini-magnetosphere of its own in Jupiter’s magnetosphere, partially shielding the satellite from plasma bombardment. The interaction between Ganymede’s magnetosphere and Jupiter’s magnetosphere is similar to the interaction between Earth’s magnetosphere and the solar wind, where magnetic reconnection plays a key role.”

Ganymede also exhibits evidence for a subsurface ocean. In contrast to Europa, an ocean in Ganymede may be bounded both above and below by ice rather than rock; nonetheless, it is likely to illuminate processes that may produce habitable environments elsewhere in the solar system (or maybe on Ganymede itself). Ganymede’s surface suggests a complex geologic history (see Figure 2.12) with similarities to those of Miranda and Enceladus. Moreover, some of its geologic terrains may be analogous to terrestrial features, thereby providing a bridge between silicate and icy bodies that could well provide fundamental information regarding the behaviorof ice in geologic processes.

Ganymede’s geologic activity and magnetic field are probably powered by tidal heating. The decadal survey states that “Ganymede’s differentiated interior and actively convecting core (required to generate its magnetic field) may be a consequence of its passage into resonance, while Callisto has not experienced this history”. Thus, better understanding of Ganymede could provide information about the tidal history of the entire Jovian system.

Mission-Specific RecommendationsA Ganymede Observer mission that addresses fundamental goals for solar system exploration may be possible and would also enable broader goals within the Jovian system. Consequently, such a mission should be included in the next New Frontiers announcement of opportunity. Because the Ganymede Observer was not described in significant detail in the decadal survey, the committee chose to list science objectives that such a mission could address, but stresses that this list should not be exclusive. In no case should these science questions be consideredto be mission requirements—they are merely options for such a mission. This list includes far more science than can be included in a single New Frontiers mission and the committee stresses that it fully expects those proposing such a mission to choose among these science objectives. It will be up to the proposers to make the case as to why some science objectives are more important than others. These objectives, which are not prioritized, include:

• Understand Ganymede’s intrinsic and induced magnetic fields and how they are generated, and characterize their interaction with Jupiter’s magnetic field.• Determine Ganymede’s internal structure, especially the depths to and sizes or thicknesses of the probable metallic core and deep liquid water ocean, and the implications for current and past tidal heating and the evolution of the Galilean satellite system as well as ocean chemistry.• Understand Ganymede’s endogenic geologic processes, e.g., the extent and role(s) of cryovolcanism, the driving mechanism for the formation of the younger, grooved terrain, and the extent to which Ganymede’s tectonic processes are analogs for tectonics on other planetary bodies (both icy and silicate).• Document the non-ice materials on Ganymede’s surface and characterize in detail the connection between Ganymede’s magnetosphere and its surface composition (e.g., polar caps).• Document the composition and structure of the atmosphere, identifying the sources and sinks of the atmospheric components and the extent of variability (spatial and/or temporal).

Under a New Frontiers budget it is likely that the most feasible way to address these objectives is by a Jupiter-orbiting spacecraft with multiple Ganymede flybys—in other words, the spacecraft may not have to enter Ganymede orbit. Even so, it is possible that such a mission may exceed the New Frontiers cost cap. Nevertheless, innovative approaches might be able to circumvent these problems and enable fundamental Ganymede science under New Frontiers constraints.

Sunday, August 9, 2009

A few blog entries ago, I gave a summary of tidbits from the recent EJSM instrument meeting. As part of that entry, I reproduced a chart (shown below) that showed what kinds of science might be done from a Galilean moon observer (GMO) that conducts multiple moon flybys but orbits none. This could be a fall back plan if the Jupiter Europa orbiter (JEO) proves too expensive at $3B+.

Bruce Moomaw wrote me to remind me that a GMO would seriously compromise the goals for Europan exploration:

"The trouble with substituting multiple Europa flybys for a Europa orbiter is simply that the single most important task for the Europa Orbiter -- beyond confirming that Europa does have a liquid ocean and might be habitable -- is to find the best possible place for followup Europa astrobiological landers, both in scientific value and in safety. And you've seen for yourself from that chart how extremely little of Europa's surface would be surveyed by 6 flybys. If we don't launch a Europa orbiter in the 2020 or so period, we will definitely have to launch one later in any case to survey Europa. (There are analogies with the need to fly one or more organic-detecting Mars rovers before we fly a Mars sample return.)"

I fully agree with Bruce that Europa should be orbited. However, wishes don't always come true. The United States is saddled with large and growing budget deficits. NASA's manned spaceflight plans are seriously underfunded. Our home planet needs more attention from a new generation of Earth observation satellites. And short of Congress adding significant money to NASA's planetary budget, we can't afford both a JEO and an aggressive Mars program. So JEO may never fly. A GMO, though, might be possible at ~$1-1.5B, or the price of a mid range Mars rover.

Observer missions to Io and Ganymede have been made priorities by NASA's scientific advisory boards (and both are possible targets of the next New Frontiers or Discovery selection, although the selection of JEO as the next Flagship mission may make this opportunity mote for these mission concepts). If JEO doesn't fly, then it's not hard to imagine that a Europa observer would make the list.

What might a GMO mission look like? I'm not a mission planner (although that would be a hell of a fun job). Here are some ideas, though:

The tour begins with a small number of Io flybys

The next target would be a series of Europa flybys that would pass low over the surface so that the ice penetrating radar can sample ice depth at several locations.

Following Europa, the spacecraft moves out of the high radiation belts and begins a campaign of Ganymede and Callisto flybys.

In an expected mission extension, the spacecraft returns to flybys of Europa to extend high resolution mapping (perhaps with a different side of Europa illuminated) and more probes of the ice depth.

I believe that if more money was possible (but still not enough for JEO), I think that a dedicated Io observer would be a good bet. A second craft would eliminate the need for GMO to be exposed to the intense radiation surrounding Io. A Io observer could also carry instruments optimized to measure the surface, atmosphere, and possibly plumes of Io. This second craft would also be in a polar orbit around Jupiter, allowing complementary magnetosphere measurements with the equatorial GMO orbit.

A mission focused on satellite flybys would undoubtedly be optimized to provide more high resolution coverage of the moons than listed in the chart above, especially for the ice penetrating radar at Europa. From a flyby mission, we would likely learn whether the average depth of Europa’s crust is thin (which would make life much easier since organic molecules produced on the surface could more easily migrate into the ocean) or thick or a heterogeneous mixture of thicknesses. The biggest loss would be that we would likely not discover locations – if they exist – where the crust is much thinner than is typical. That science requires an orbiter. I hope one flies in my lifetime (which should last another 30+ years). If not, I’d rather see an Galilean satellite observer than no mission to these moons at all. I would make the same point about a follow up mission to Enceladus and Titan.

Friday, August 7, 2009

By far, the most interesting presentation at the last MEPAG meeting was an analysis of options for a 2018 mid-range (between MER and MSL in capabilities and cost) rover (MRR) as a precursor to MSR. It's a long presentation that takes a couple of readings to digest. This will be a summary of key points. I urge you to read the presentation if you are interested in the details of Mars mission planning. (MER = Mars Exploration Rovers Spirit and Opportunity; MSL = Mars Science Laboratory Curiosity; MSR = Mars Sample Return.)

The mission plan wrestles with several key requirements imposed by NASA's larger Mars program goals. First, the mission needs to continue the goal of exploring past or present questions of habitability. Second, it needs to fit within a larger goal of an eventual sample return. Third, it needs fit within a budget of ~$1B plus a bit. And fourth, it must be a precursor to MSR.

From a long list of possible scientific goals, three were selected:

* Explore Noachian (the earliest period of Mars history around 4.6 -3.5B years ago) to determine if life arose on Mars and to explore the environment in which it either did or did not arise* Explore the transition from the Noachian to Hesperian (3.5-1.8B years ago) to understand how the Martian environment changed* Explore questions of astrobiology in a new location different than the ones that will be explored by the MSL (slated for a 2011 launch) and the European ExoMars rover (also slated for 2018).

The definition team also added a forward looking programmatic goal: cache samples for a future Mars sample return mission to return sometime in the future (hoped to be in the 2020s). This goal comes with a hefty scientific price tag. The potential weight of the scientific instruments drops from 40+ kg to just 15 kg. The difference would go to equipment to acquire, handle, and store approximately 20 sample cores. (A graphic suggests that 5 samples might be taken from 4 sites along a traverse.)

To fit within the weight limit, the scientific instruments would be largely placed on a robotic arm, much like MER's are. (Like MER, the MRR would have mast mounted cameras and possibly spectrometers but would not have MSL's laser-induced breakdown spectroscopy.) Sophisticated chemical and biological laboratories such as those carried by MSL and ExoMars would not be possible.

However, the instruments carried on the arm would be much more sophisticated than MER's. The latter's instruments take average composition readings across the target zone. MRR's instruments would conduct “micro-mapping” across the target zone , allowing study of composition of small areas within the target zone. (If this is unclear, remember that MER uses its grinding tool (the RAT) to remove the surface rind from a small target area. Then different instruments are placed against the target zone. MER's microscopic imager has shown that the RAT'ed areas are full of fractures, inclusions, layers, blueberries, etc. that each have their own story to tell. MRR's instruments would be able to examine each of these micro areas individually.)

Several advanced arm-mounted contact instruments are proposed to enable microscale visual, mineralogical, organic, and elemental imaging. Perhaps the most important of these would be two flavors or Raman spectrometers that can detect the presence of organic material present in parts per billion.

To round out the summary of the mission, it would be solar powered, limited to equatorial regions, and would reuse MSL's precision descent and skycrane landing technologies.

Site selection for this mission would have be done not only to explore ancient potential habitats for life. Because samples will be cached for future retrieval, a whole new set of site selection criteria such as stratigraphy, evidence for ancient atmospheres, and remnant magnetism come into play.

Editorial thoughts: The mission proposed is ambitious. It's targeted for $1B plus a bit. I would not be surprised to see that bit grow by $500M to $1B.

Readers of this blog know that I believe that a sample return mission will fly shortly after the true location of Shangri-La is found. Devoting substantial weight to caching samples forecloses two other potential strategies:

* Flying a sophisticated astrobiology laboratory as will be done for MSL and ExoMars. That laboratory would add to our scientific understanding of Mars. If those samples are never returned, that data that will never be recovered.* Flying two smaller rovers that also forgo the astrobiology instruments but that carry the sophisticated contact instruments proposed for the MRR. This alternative would give us the opportunity to explore two different sites.

I think that the most important decision to come out of the Decadal Survey in progress is whether or not to bet the Mars and planetary program on a $6B sample return that would largely consume the planetary exploration budgets for approximately a decade. If the decision is that those samples are that important, then the proposed MRR looks reasonable. If Congress and NASA aren't willing to make that bet, then there are other strategies for MRR that could be pursued. This is the first mission where serious trade offs would be made based on whether or not a sample return mission will be flown. This is gut check time.

Thursday, August 6, 2009

The last MEPAG meeting had a full agenda with lots of information on future Mars plans.

Marcello Coradini from ESA presented that agency's current plans for the 2016 and 2018 missions. As related in previous posts, the current plan is for NASA to launch an ESA trace gas orbiter and engineering entry and descent test in 2016. In 2018, NASA will launch a mid-range rover of its own and ESA's ExoMars rover; the 2016 orbiter will provide data relay. The 2016 lander will be strictly an engineering test powered by batteries with only test instrumentation and a camera. (And since the current idea is to send the lander to an utterly safe destinations like Meridiani, don't expect exciting new vistas. The lander design could be reused for a 2020 network landers mission. The presentation states that more money will be needed for this new plan than the old one. Per the Nature article (see previous post), it looks like the additional money may be available since the ESA member states have given their okay.

Editorial thoughts: The new Mars plan is starting to sound quite ambitious. I am concerned that (1) missions will keep within their cost targets (rovers are hard and biology instruments probably more so) and (2) the additional funds will be available. I hope that I'm wrong.

About Me

You can contact me at futureplanets1@gmail.com with any questions or comments.
I have followed planetary exploration since I opened my newspaper in 1976 and saw the first photo from the surface of Mars. The challenges of conceiving and designing planetary missions has always fascinated me. I don't have any formal tie to NASA or planetary exploration (although I use data from NASA's Earth science missions in my professional work as an ecologist).
Corrections and additions always welcome.